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Old 07-25-2021, 10:56 AM
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Originally Posted by John Milner View Post
Thanks for the replies everyone. It sounds like as long as I can get some bearings, it really wouldn’t be a big deal turning one .040 on the rods. I’ll be sure to get some bearings in hand before the crank gets ground.
Years ago I knew a dragster who built many engines for the strip. He told me if you cut a crankshaft more than .030, the bearings will be too thick and heating issues would result. Perhaps bearings have improved since then but there is something in what he said.

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Old 07-25-2021, 11:55 AM
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Sounds like old time BS to me!
When bearings are made thicker they do so by making the main steel back thicker, not the bearing overlays which might block heat, so heat transfer is still the same .
Oil flow onto the Jurnal and out is what removes the greater portion of the heat load anyway and less bearing speed always results in less heat, so once again pure BS on that builders part, either that or he full well new the performance pluses of smaller crank pins and wanted to keep this to his benefit!

It’s called counter intelligence when governments use this practice.

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Old 07-25-2021, 01:23 PM
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Originally Posted by steve25 View Post
Sounds like old time BS to me!
When bearings are made thicker they do so by making the main steel back thicker, not the bearing overlays which might block heat, so heat transfer is still the same .
Oil flow onto the Jurnal and out is what removes the greater portion of the heat load anyway and less bearing speed always results in less heat, so once again pure BS on that builders part, either that or he full well new the performance pluses of smaller crank pins and wanted to keep this to his benefit!

It’s called counter intelligence when governments use this practice.
As an auto tech with over 40 years in the field, I agree with Steve25. I call BS on the 'old time mechanic' as well.

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Old 07-25-2021, 03:51 PM
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Hmmm. Not that I have much to add on this, but from memory, deep dark memories. At one time (maybe 1950s into the 60s), undersized bearings had the same steel shell and the Babbit was thicker. When put up to a bunch of force they distorted and create heat. An “old timer” machinist that did performance work from that era would have likely used that rule.

Then came the “anything under .010”/.010” was frowned on for performance stuff rule”, the bearings changed to a thicker backing (as Steve25 mentioned) but some machinists kept the rule. Then instead of the thick babbit being the reason, that .010”/.010” followed for fear of cutting through the nitriding.

Have heard some of the aftermarket nitriding is super shallow, .005” goes through it. FWIW. My opinion is the same as most everyone’s… cut the crank down and run it….But good luck finding .040” under bearings, I think it would be easier to find and other crank.

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Old 07-26-2021, 11:58 AM
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Originally Posted by Jay S View Post
Hmmm. Not that I have much to add on this, but from memory, deep dark memories. At one time (maybe 1950s into the 60s), undersized bearings had the same steel shell and the Babbit was thicker. When put up to a bunch of force they distorted and create heat. An “old timer” machinist that did performance work from that era would have likely used that rule.

Then came the “anything under .010”/.010” was frowned on for performance stuff rule”, the bearings changed to a thicker backing (as Steve25 mentioned) but some machinists kept the rule. Then instead of the thick babbit being the reason, that .010”/.010” followed for fear of cutting through the nitriding.

Have heard some of the aftermarket nitriding is super shallow, .005” goes through it. FWIW. My opinion is the same as most everyone’s… cut the crank down and run it….But good luck finding .040” under bearings, I think it would be easier to find and other crank.
This is exactly what my mechanic racer was saying. Not BS guys and back when he was building engines for the strip he and many used that .010" rule. However today it seems the bearings are designed differently and perhaps there is no longer a heat issue. Regardless, removing more than .030" from the crank is a lot and I wouldn't do it unless the crank was rare. Now for the street, I don't see any issues but on a strip car running high revs, I would be a bit concerned!!!

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Old 07-26-2021, 02:25 PM
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Your comment on weaking the crank by cutting it over .030” has no logic to it since new cast iron Cranks are sold with BBC size rod journals .

Now let’s take this new Cast Crank in BBC size a step further, you have a problem and have to cut the Crank .020” on the Rods, so now where’ are you strength wise as compared to a stock Pontiac Rod journal?
Folks don’t seem to bat a eye at this now do they.

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 07-26-2021 at 02:32 PM.
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Old 07-26-2021, 03:22 PM
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Originally Posted by geeteeohguy View Post
As an auto tech with over 40 years in the field, I agree with Steve25. I call BS on the 'old time mechanic' as well.
Been over 50 years since I worked in my uncle's Pontiac Dealership on a couple of Ram Air IV engines. Both were bearing jobs and one was a completely different (replacement) RA-IV block. Under Warranty.

Now we had a Mechanic who taught Mechanics to soldiers in World War II, I have mentioned him in the past: Delbert Forrest. He said they have had the normal bearing shell thickness increase for oversize bearings (since the mid 50s, 1956 Pontiac comes to mind), But they did things differently prior to World War II. SO YOU MAY BOTH BE CORRECT ON THIS ONE, JUST ARGUING OVER THE TIMELINE.

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Old 07-26-2021, 03:30 PM
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Could be!

But even up to 1930 it was common if you needed new bearings for shops burn the babbitt off the steel backs of shot bearings and pour in new babbitt and you could make it as thick as you wanted before machining it down to what you needed.
Who knows how much some cranks where cut and how thick Babbitt was poured to try and save a motor?

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 07-26-2021 at 03:43 PM.
  #29  
Old 07-26-2021, 07:02 PM
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Our Dealership got a few "reman" cranks with bearings for warranty work on 400's. these were usually Turned on mains and rods or both.
They had a tag on the stating that they were "Re Tufftrided" , ferritic nitrocarburizing to get technical.
I'm not sure how deep this 1000 degree salt bath process makes the surface hard, but I was told by '82 they were switching to "Nitriding", which made the hardening Deeper in the metal.
SO Turning an old crank to -.040 may work fine, but I am going to guess that the Trufftriding is gone.

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Old 07-26-2021, 08:54 PM
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I am totally amazed that a cast-iron crank has any sort of surface hardening.

Forged steel crank--sure. Cast iron--I wouldn't have guessed.

  #31  
Old 07-27-2021, 03:03 AM
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Originally Posted by Schurkey View Post
I am totally amazed that a cast-iron crank has any sort of surface hardening.

Forged steel crank--sure. Cast iron--I wouldn't have guessed.
These could have been Forged, but sure didnt look it. We had a few SR engines still under warranty in 77 from 1970 cars.

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Old 07-27-2021, 05:45 AM
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Bruce, I call BS!

The only way to surface harden cast iron is by electric induction hardening like they started to do with the valve seats once lead got taken out of the fuel.

Also the induction process is very expensive equipment wise in and of itself and then add to that the difficulty of trying to apply it to a crankshaft places it extremely out of the range of what a Crank grinding shop would be able to do and no less make money on!

I think that dealership that you where working at was getting billed and ripped off by paying for a process that could simply not be done to a factory cast Crank, and even if they where dipping the cast Crank in a hot salt bath that process did nothing to surface harden the Crank!

Let me add this also, with a steel Crank put through the salt bath process many times due to the temperature swing the Crank bends some and needs to be straighten in a jig by someone trained in how to do this and doing this to a cast Crank would in the least put stress cracks in the Crank or just Crank it right then and there!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 07-27-2021 at 06:00 AM.
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Old 07-27-2021, 10:16 AM
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FWIW…I am kind of cautious about making broad statements about what kind of surface treatments can be done to crankshafts. It is dependent on what the metallurgy is. A lot more options than induction hardening. A medium to low grade cast crank could be Tuffrided, a lower temp version thinner version of Nitriding. IRC, a Nodular or Arma steel could be nitrided. The better the crank material the more apt it is to working better. A low grade material like a new aftermarket cast crank is to low grade of steel and won’t take to nitriding, doesn’t bond right with the surface and chunks off, but it might be able to go through an alteration of a Tuffriding process. Probably the better solution if strength is the concern on a cast crank is sending it off and having it cryo’ed versus surface treatments. Jmho

Just by grinding a crank the journals get work hardened some and will have a little higher Rockwell test than the rest of the crank. But nitriding&tuffriding increase the hardness more yet. There are different reasons for surface treatments. I would not know what Pontiac did, but it wouldn’t surprise me at all if any OEM tuffrided reman cranks. Anti-wear properties are likely the main reason why OEM’s would use those types of surface treatments. It certainly helps strength by making the surface resistant to cracks, but if the crank is going to brake with no nitriding, it will still brake with nitriding. Just will take more cycles to brake.

My T/A runs a 455 N crank with the mains cut down from 3.25” to 3”, plus has 2.2” BBC journals, offset ground to 4.25” stroke. Probably 550 hp or more. Makes a .040” crank cut look modest.


Last edited by Jay S; 07-27-2021 at 10:18 AM. Reason: Err
  #34  
Old 07-27-2021, 01:29 PM
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Based on the way warranty worked, I am guessing these tags were put on any crank, just to make sure techs knew it was ready to install.
They all did get something Im sure, they wouldn't send out a crank for a SR 1970 engine and not have it ready.
The folks at my dealer I could ask about this have passed long ago.
I did a bunch of crank, shortblock , long block work at my dealership.
My Last stint in that realm was the Quaker state Motor oil debacle.

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Old 07-27-2021, 05:54 PM
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When I was in my Uncle's Pontiac Dealership, we used Wolf's Head oil in 55 gallon drums.
My uncle would not touch Quaker State Oil or the off shore oils like Shell.

Tom V.

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Old 07-27-2021, 11:27 PM
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I still have a few sets of H beam 6.625 long rods that are BBC 2.200 journal on the big end and set up for a .980 pin. Or hone pin end to .990. Had them made years ago for the warn out rod journal cranks because even 15 years ago it was hard to find .040 bearings. PM me if you need a set. They weigh about 777 grams if I recall. 7/16 cap screw ARP 8740 bolts 1.800 Long. Finished machined in house big and small end.

As far as surface hardening the nodular/pearlitic malleable iron/ armasteel cast cranks my favorite way is ionitriding. Doesn't open up the pores in the nodular iron as much as the ammonia gas nidriding.

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Old 07-28-2021, 06:03 AM
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Why are many of you so happy to have a procedure applied to cast Crank that does not strengthen it one bit, in fact the surface hardening that is developed has been proven to be a great beginning point for a crack to start?

I would much sooner go thru the added effort of keeping my oil flowing over my cast Crank nice and clean to limit ware and run a Bearing with better embedding characteristics!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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Old 07-28-2021, 07:41 AM
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What is everyone’s opinion on running a crankshaft that has been cut .040 on the rods? My N crankshaft is a little rough and the crank grinder thinks it will take .030 or .040 to clean it up. I’ve always ran std or no more than .020 under on the rods. .040 sure seems like a lot. The engine is a 68 WS 400 and will likely never see over 5,500 rpm and not be over 400 horsepower.

Look what you started

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Old 07-28-2021, 07:47 AM
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Why are many of you so happy to have a procedure applied to cast Crank that does not strengthen it one bit, in fact the surface hardening that is developed has been proven to be a great beginning point for a crack to start?

I would much sooner go thru the added effort of keeping my oil flowing over my cast Crank nice and clean to limit ware and run a Bearing with better embedding characteristics!
Many years ago we used to have our race cranks "heat treated". The process would usually warp the crank a bit and we would straighten it. The heat treat definetly seemed to help with bearing wear. Never had an issue with any of the cranks we did. In fact atleast two of them are still in service today. Later we used a bunch of hard chromed cranks. The bearing wear on those were excellent and the journals never measured any wear.

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Old 07-28-2021, 08:22 AM
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Later we used a bunch of hard chromed cranks. The bearing wear on those were excellent and the journals never measured any wear.
Barney Moravitz, and later Jim Butler, had a bunch of Pontiac Cranks done that way. Course this was 30+ years ago

Tom V.

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